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LONDON, England (CNN) -- All four men suspected of planting failed bombs on London's transit system on July 21 are in custody after raids in London and Rome, according to sources close to the investigation and Italy's interior ministry.

Peter Clarke, head of the Metropolitan Police Anti-Terrorist Branch, read a statement confirming four men were arrested Friday, three of them in London and one in Rome, but did not identify them as suspected bombers.

British authorities have refused to describe the men's possible ties to the attempted bombings, saying it could prejudice their right to a fair trial.

Clarke said one of the men arrested in London identified himself to police as Ibrahim Muktar Said, whom police had previously named as the suspect who planted a backpack bomb on a double-decker bus in Hackney, East London, on July 21.

Clarke said the man arrested with Said at a flat in Peabody Buildings, Dalgarno Gardens, identified himself as Ramzi Mohammed. Sources close to the investigation told CNN's Henry Schuster two of the three wanted bombers were arrested at Dalgarno Gardens, a government-subsidized apartment building in West London.

Another man was arrested in Tavistock Crescent, in West London, Clarke said, and he will be questioned in relation to the July 21 attacks.

Clarke also confirmed that Italian authorities have arrested "another man of interest" to the investigation, Hussain Osman, in Rome.

A statement on Italy's Interior Ministry Web site identified him as a naturalized British citizen of Somali descent.

He is believed to be the man who attempted a bombing at the London Underground's Shepherd's Bush station.

Clarke said Britain was seeking Osman's extradition from Italy.

British authorities also arrested Yasin Hassan Omar, another Somali with British residency, in Birmingham. Police said the 24-year-old was suspected of placing a backpack bomb at London's Warren Street Underground station.

Clarke added though that despite progress made in the investigation, the terrorism threat remains "very real."

Two weeks before the failed attacks, bombs on three subway trains and a bus killed 56 people, including four suicide bombers.

London arrests

Dramatic video obtained by ITN of Friday's raids in London showed Ibrahim and Mohammed, said by police sources to be Oval Station bomb suspect, with their shirts off and hands in the air.

Before the men came out, the video showed police with gas masks two stories below entering another flat. One of the officers was temporarily distracted by two unafraid children.

One woman, who would not reveal her name, said she heard the entire three-hour exchange between the suspects and police, who had called for "Muhammed" to come out of the building. (Eyewitness accounts)

"Police started to say to him you need to come out of the flat ... with your underwear on and your arms up in the air," she told reporters. "He was then saying to them, 'How do I know that you're not going to ... shoot me?'

"They said you need to come out into the street with your underwear on so that we know that you haven't got any explosives on you, and so that we know that you're not a risk to the police or the public."

She said she heard the exchange from her apartment window, and the man sounded like he may have been crying. After he stopped talking to the police, she said, "a more aggressive police officer got on the loudspeaker and started saying to him, 'You need to maintain contact.'"

"He didn't maintain contact. And after a while you started to see the SWAT teams arriving ... and once they came out, and after about 15 minutes of not having contact with him, you heard like the gunshots go off."

Another raid took place in Notting Hill where another man was arrested. British Transport Police said two women were also arrested under the Terrorism Act at Liverpool Street station just before 2 p.m. (1300 GMT).

A few minutes later, the station -- a major train and subway hub in the city's financial district -- was evacuated following the discovery of an unattended suitcase on the main station concourse. The station reopened shortly after 3 p.m.

The location of Friday's operation in west London is about one mile from Little Wormwood Scrubs Park, where police found a fifth undetonated bomb three days after the attempted July 21 bombings.

Police said the bomb was in a plastic container identical to the four partially-detonated devices left on three tube train cars and double-decker bus.

The neighborhood is also a little over a mile from the Shepherd's Bush Underground station, where one of the July 21 bombers failed to detonate a his bomb, then fled, running on a course in the direction of this park.

On Thursday, police arrested nine men in the Tooting area of south London.

Six were detained at one address and three at another, according to Metropolitan Police.

Rome arrest

The arrest of Osman in Rome came in a joint operation between Scotland Yard and the Italian police, a seniorItalian intelligence source told CNN.

Scotland Yard tipped off the Italian authorities and were able to trace Osman's cell phone as he travelled from London to Rome, CNN's Jennifer Eccleston said.

The cellphone, which authorities said belongs to Osman's brother-in-law, helped track Osman to a Rome apartment in an area known as Casilino -- a neighborhood heavily populated by internationals, primarily North Africans.

The source said he believes the suspect came to Rome because it is easier to hide in the city -- which has a larger Somali population than does London.

The source said a second man in the apartment -- a Somali citizen later identified as Osman's brother -- was also taken into custody for questioning. He owns a call center at Termini, Rome's main rail station.

Eccleston said it was not clear when Osman left London for Italy, but he is thought to have stopped in the northern cities of Milan and Brescia, before heading to Rome.